Nelson, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 3.9 °C (low) to 15 °C (high). Annual precipitation averages 1002.3 Millimeters. Nelson is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -10.6 °C | -1.5 °C | 44.2 mm |
| February | -8.5 °C | 1.1 °C | 44.96 mm |
| March | -2.7 °C | 8 °C | 61.21 mm |
| April | 3.2 °C | 15.5 °C | 94.74 mm |
| May | 9.8 °C | 21.8 °C | 125.98 mm |
| June | 15.3 °C | 26.8 °C | 136.91 mm |
| July | 17.1 °C | 28.4 °C | 109.47 mm |
| August | 15.9 °C | 27.6 °C | 107.44 mm |
| September | 11.3 °C | 24.4 °C | 96.01 mm |
| October | 4.8 °C | 17.2 °C | 71.88 mm |
| November | -1.4 °C | 8.7 °C | 59.18 mm |
| December | -6.9 °C | 1.7 °C | 50.29 mm |
| Annual | 3.9 °C | 15 °C | 1002.27 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5b : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |